Electronic cigarettes and cartridges that contain their vaporizable liquid in a “tank” structure or reservoir have performance and usability advantages over those which hold the liquid inside of a sponge or other medium. Unfortunately, tank-type cigarettes and cartridges have some unique difficulties associated with filling them. These problems are particularly acute because of the need for a porous wick that is in contact with the tank in the cartridge and/or electronic cigarette.
For example, tank-type cartridges may leak when subjected to a change in atmospheric pressure (such as may occur during air shipment), which can cause liquid to leak through the necessary porous wick, due to expansion of any captive air. If the cartridge could be filled completely with no captive air, this issue can be eliminated, at least at the time of initial shipment. As a result there is significant incentive to attempt to fill the cartridge as completely as possible.
There are currently two main approaches to filling a tank-type cartridge. The first approach is to make use of one or more elastomeric “plug” components that are removed and leave sufficient clearance at the time of filling that any air that is captured in the cartridge is able to freely vent through the same hole or holes that liquid is being added to. A secondary operation is required to install the plug, along with in many cases an additional cosmetic part that conceals the plug.
Unfortunately, the approach of filling with a plug part removed has a few problems. First, it requires that the cartridge be partially disassembled at the time of filling. This can result in supply chain complexity of shipping components separately as well as additional costs associated with the additional capping operation, especially if the cartridges are assembled in different locations as is often the case where it may be cheaper to manufacture in a first location and assemble in a second location. Second, a plug may potentially take up volume in the cartridge, and finally, inserting the cap my itself displace fluid and introduce air; inserting the plug may force the displaced volume of liquid through the porous wick to the outside of the tank area. The non-zero time between the filling operation and the capping operation can create a potential failure mode where liquid is allowed to slowly leak out through the wick without the negative backpressure provided by the sealed reservoir. The amount of liquid that can leak through during even a controlled time frame is a function of the viscosity of the liquid (which can be variable based on the liquid used) and therefore can be difficult to control.
The second approach, discussed in patent application no. WO2015028815 A1, is to use a sufficiently large elastomeric component of sufficiently low durometer that it can be pierced simultaneously by two hypodermic style needles whose pierce sites will reseal sufficiently after the needles are removed. This approach assumes an effective seal between the elastomeric component and the filling needle but requires a second, venting needle. One needle is described as being the inlet for liquid into the interior of the cartridge, while the other for the evacuation of the air that is inside the cartridge before filling. This approach allows the cartridges to be fully assembled at the time of fill.
Although this two needle approach may alleviate the need to perform a separate capping operation, it also has issues in terms of its ability to fill the cartridge completely and with a precise volume of liquid. Each pierce location is a potential failure site in the final product, and thus using a secondary vent pierce site doubles the chance of a problem with the final product and during the piercing process. In addition, if passive venting is chosen through the second needle, the level of fill must be sufficiently low to prevent liquid ever reaching the second needle, because although air can easily vent through the small diameter needle; liquid in the needle constitutes a significant blockage. Once liquid enters the second needle, air may no longer flow, even if still trapped within the electronic cigarette or cartridge reservoir. If active venting is chosen, there is a similar risk that the vacuum will pull liquid out of the cartridge, causing waste and introducing additional randomness to the final fill volume.
Finally, in all cases the secondary vent pierce limits how full the container can be filled since the needle has to pierce sufficiently deeply to ensure that it's opening is fully below the surface of the elastomeric component, which inherently means that there is some cavity of air left above it that can never be displaced. This issue persists even if a production method is created that can tolerate the liquid front reaching all the way to the vent location. Once the liquid front reaches the vent location any incremental liquid added to the system either gets forced through the vents or through the porous wick to the outside of the tank.
For example, FIGS. 1A-1G illustrate the use of the current two-needle approach and its shortcomings. In this example, the cartridge includes an elastomeric cap, and is preassembled with the wick, polymeric reservoir (rigid tank), and elastomeric (piercable) resealable cap. In FIG. 1A the assembled cartridge is ready to be filled by receiving the needles. In FIG. 1B the needle pierces the elastomeric cap to a distance that is large enough to ensure that the needle opening is exposed and open within the cartridge, then begins to fill. In FIG. 1C, the front of liquid being filled reaches one end of the cartridge and one side of the wick. In FIG. 1D the liquid front has occluded both sides of the porous wick. In FIG. 1E the liquid front has risen until it is nearly at the vent needle. This may be an ideal time to stop if (e.g., passive filling) the needle will clog and stop passing air once fluid contacts it (e.g., cannot tolerate liquid in the vent line). In FIG. 1F the liquid front has occluded all of the vent locations, and any incremental liquid pumped into the cartridge past this point (even with active venting through the vent needle) will either pass through the vent needle or leak out of the porous wick. No additional air can be displaced. Finally in FIG. 1G, once no more liquid can be added to the system, the needles are retracted and the filling is complete, leaving a substantial amount of captive air.
Thus, there is a need for methods and apparatuses (e.g., cartridges, filling devices and the like) for filling electronic cigarette and/or cartridge reservoirs so that they do not trap any air within the otherwise sealed reservoir, and particularly in reservoirs including a porous wick. Described herein are methods and apparatuses to address this need.